School of Engineering Department of Civil and Environmental Engineering 87 Recyclable Hydrogel-Based Brick for Construction on Mars: A Feasibility Study Supervisor: QIU Jishen / CIVL Student: NGAN Man Cheuk / CIGBM Course: UROP4100, Fall This study aims at investigating the efficiency of different recycling approaches for the hydrogel-based bricks and their impact to the gel’s mechanical properties after recycling. Our research object is Gelatin as it provides high recyclability with little requirement of additional chemical agents and environment condition. Compression tests and SEM analysis are conducted to examine the impact of recycling bricks to the stress, elastic modulus, and failure modes of the bricks. The 2 nd Generation bricks made with the recycled materials from the 1st generation bricks and water exhibit similar mechanical properties and can achieve a compressive strength of 9.083MPa, which is about 87.8% of the original strength before recycling. Another recycling method in which the hydrogel is extracted into a solution form and mixed with new ceramic beads can maintain a compressive strength of 6.55MPa, which is about 63% of the strength of 1st generation bricks. A Cement-Free Novel Concrete that Absorbs Greenhouse Gas Co2 to Heal Itself and Improve its Mechanical Performance. Supervisor: QIU Jishen / CIVL Student: LEE Yin Ni / CIGBM Course: UROP1100, Spring UROP2100, Summer Reactive magnesia (MgO) is a promising alternative to conventional Portland cement (PC) as it could potentially recapture carbon emissions from concrete production. However, inadequate carbon dioxide (CO2) diffusion for carbonation and thus strength development remains a major technical challenge for the industrial application of reactive MgO cement (RMC) as concrete binder. Previous works have found hollow natural fibres (HNFs) effective in establishing CO2 transportation channels to enhance CO2 penetration and thus carbonation in RMC-based composites, however, such channels might be blocked by water, especially in composites with high water-to-binder (w/b) ratios. To counteract this effect, RMC-based composites were dried for different durations after demoulding to lower free water content and facilitate carbonation at core regions in the subsequent curing process. This study found that a balance in w/b ratio and drying duration could provide the ideal formulation of HNF-added, RMC-based composites with enhanced carbonation, such that RMC-based composites could potentially substitute PC-based matrix as a net-zero concrete with the possibility of complete utilisation of RMC’s carbon sequestration capability.